Climate change due to increasing amounts of greenhouse gases in Earth's atmosphere poses one of the greatest threats to mankind and world's ecosystems as a whole. Carbon dioxide (CO2) is one of the most significant contributors to climate change, making up approximately 77% of the world's greenhouse gas emissions by some estimates. Many of the CO2 emissions are due to, for example, combustion from power plants or other industrial facilities.
There have been numerous methods and systems developed in attempts to reduce and/or eliminate these emissions. Such methods include carbon capture and storage or sequestration. Such methods often rely on separating (i.e. capturing) CO2 from, for example, combustion gas or other CO2 sources. Unfortunately, in order to be effective the captured CO2 must then be disposed as opposed to released to the environment. The disposal methods developed thus far are very inadequate. For example, one such disposal method employed is compression followed by, for example, delivery to an underground geological formation or other manner of containment. In another method carbon dioxide is captured by ammonia and used in a forward osmosis process with high temperature and pressure. Unfortunately, such current methods often require complex apparatuses, are expensive to implement, consume vast amounts of energy, and/or usually do not yield usable or saleable products.
It would therefore be desirable to determine new methods for reducing and/or eliminating CO2 emissions. It would further be advantageous if such new methods could be implemented using less complex equipment, were cost-effective, consumed less energy, and/or yielded usable or saleable products. Advantageously, the instant processes accomplish one or more up to all of the aforementioned.
In one embodiment the invention pertains to an integrated process for generating energy and useful nitrogen compounds from captured carbon dioxide. The process comprises forming a solution of ammonium carbonate, ammonium bicarbonate, ammonium carbamate or mixture thereof. The solution is formed from at least a portion of captured carbon dioxide. The solution of ammonium carbonate, ammonium bicarbonate, ammonium carbamate or mixture thereof is decomposed to form ammonia, carbon dioxide, a precipitate, or a mixture thereof. The decomposing of the solution is further characterized by one or more of the following:
(a) decomposing such that ammonia and carbon dioxide are formed in a molar ratio suitable for production of ammonium carbamate, urea, or a derivative thereof;
(b) decomposing at about atmospheric pressure;
(c) decomposing in the substantial absence of high temperature equilibrium;
(d) decomposing using low grade heat;
(e) decomposing in the presence of a semipermeable membrane, condensing, or a water soluble, solvent under suitable conditions to form substantially separated ammonia and carbon dioxide; or
(f) decomposing under conditions to form a precipitate comprising a salt of carbonate, bicarbonate, carbamate, or a mixture thereof.
In another embodiment the integrated process may comprise employing an osmotic engine. The osmotic engine comprises: (1) the formed solution of ammonium carbonate, ammonium bicarbonate, ammonium carbamate or mixture thereof as a draw solution and (2) a feed solution having a lower osmotic pressure than said draw solution to generate a gradient. The gradient may be used to generate energy and a second solution of ammonium carbonate, ammonium bicarbonate, ammonium carbamate or mixture thereof wherein said second solution has a lower osmotic pressure than the draw solution and wherein at least a portion of said second solution is subjected to decomposing as described above.
In another embodiment the invention pertains to an integrated process for generating energy and useful nitrogen compounds from captured carbon dioxide comprising capturing carbon dioxide from a combustion emission stream by exposing the carbon dioxide to aqueous ammonia under conditions suitable to form a draw solution comprising ammonium carbonate, ammonium bicarbonate, ammonium carbamate, or mixture thereof. An osmotic engine is employed comprising: (1) the draw solution and (2) a feed solution having a lower osmotic pressure than said draw solution to generate a gradient. The gradient is used to generate energy and a second solution of ammonium carbonate, ammonium bicarbonate, ammonium carbamate, or mixture thereof wherein said second solution has a lower osmotic pressure than the draw solution. The second solution of ammonium carbonate, ammonium bicarbonate or mixture thereof may be decomposed to form ammonia, carbon dioxide, or a mixture thereof. The decomposing of the second solution is further characterized by one or more of the following:
(a) decomposing such that ammonia and carbon dioxide are formed in a molar ratio suitable for production of ammonium carbamate, urea, or a derivative thereof;
(b) decomposing at about atmospheric pressure;
(c) decomposing in the substantial absence of high temperature equilibrium;
(d) decomposing using low grade heat; or
(e) decomposing in the presence of a semipermeable membrane, cooling, or a water soluble solvent under suitable conditions to form substantially separated ammonia and carbon dioxide. The ammonia and carbon dioxide that were decomposed from the second solution may be reacted under conditions to form one or more useful products selected from the group consisting of ammonium carbamate, urea, or a derivative thereof.
In another embodiment the invention pertains to an integrated process for generating energy and useful nitrogen compounds from captured carbon dioxide comprising contacting ammonia, carbon dioxide or a solution made therefrom with a suitable draw solution. The contacting is conducted under conditions such that a precipitate is formed which comprises ammonia carbonate, ammonia bicarbonate, ammonia carbamate, or a mixture thereof. Suitable draw solutions may be selected from the group consisting of ammonium sulfate, ammonium nitrate, potassium carbonate, potassium bicarbonate, or a mixture thereof.